The invention relates to a method of fabricating dome-shaped dies. Typically, dies for cellular extrusions are formed from solid steel blocks by drilling feed holes in the entrance portion of the die and cutting slots in the exit portion of the die such that the holes generally intersect the slots. Dies can also be made by stacking plates which have the appropriate feed holes and slots so that they generally intersect when stacked.
Monolithic dies for extruding cellular structures are usually made using straight round feed holes which communicate from the inlet side of the die to the slots in the outlet face of the die. This is because straight round feed holes are often easier and least expensive to make. However, straight round holes can lead to problems since shoulders are formed where the holes intersect with the slots. In addition to the problem of high wear, this creates high back pressure during extrusion. There are other problems associated with the traditional method of forming dies. For example, for very thin-walled cellular extrusions which require thin slots, dies made by the above methods have proved both difficult and expensive due to the extra processing steps often required to produce useful dies. For example, it has been suggested to coat the slots in certain dies to achieve the desired wall thickness.
To avoid the sometimes abrupt changes in cross-sectional area of the feed holes at their junctions with the discharge slots, it has been suggested in co-assigned U.S. Pat. No. 5,066,215 issued to Peters et al., to form feed holes having a gradual transition of flow cross-sectional area and shape commencing at the entrance portion or end of the feed hole and terminating at the exit portion or end of the feed holes, where longitudinal and lateral flow through discharge slots commences. In the reference die, the cross-sectional area at any location along the length of any feed hole is less than at any location upstream thereof. While the suggested die eliminates the high bending forces on the die and also substantially reduces abrasive wear, it is relatively expensive to manufacture since each hole and slot combination must be cut individually.
To reduce the costs associated with such dies, in co-pending, co-assigned patent application (U.S. Ser. No. 08/021,487), I have disclosed a relatively inexpensive and easy method of making geometrically complex dies having ultra-thin slots for extruding very thin-walled cellular structures. While the method described therein reduces the cost of making such dies, there continues to be the need for easier and inexpensive methods for fabricating complex-shaped structures such as thin-walled cellular or honeycomb structures which will not deform or break under pressure.
Accordingly, it is the object of the present invention to provide a die for making complex thin-walled cellular structures which die will not deform or break under pressure, and a method of producing such die.